1. Field of the Invention
The invention relates to an apparatus for ascertaining at least one actual operating state of a magnet-valve-controlled injection pump for internal combustion engines, in particular Diesel engines, wherein pump pistons travel on a filling ramp and on a supply ramp of a cam ring, cam disk or cam shaft, and a supply onset is defined by a closure of a magnet valve.
In the future, injection pumps with a central electronically controllable valve will be used for high-speed Diesel engines with electronic control of the injection onset and quantity. In them, pistons run on a cam ring or on a cam disk or shaft, which form filling ramps and supply ramps. If the pistons arrive at the supply ramp at a time that simultaneously is supposed to be the supply onset, then if the magnet valve is closed a high pressure immediately builds up, with the consequence thereof being the onset of an injection event.
Published European Application No. 0 481 912 A2 discloses a pump type in which the closing time for the magnet valve does not match the supply onset of the pump. With that type of pump, the cams float between the closing time of the magnet valve and the supply onset time without touching a ramp, until the cams gradually arrive at the supply ramp.
That pump principle (which is also known as the fill-spill mode) is briefly explained below in conjunction with FIG. 3. In that device, the supply onset is not specified by an electronic control unit but rather is arrived at by calculations based on a numerical description of the cam geometry. A certain time elapses between the calculation and the triggering of a magnet valve closing time, in which a supply onset time might have changed and in which case the precise supply onset time is located elsewhere. Inaccuracies in calculation can also result in the actual value of the supply onset time not matching the command value.
That problem is well known. In order to solve the problem, Published European Application No. 0 481 912 A2 proposes a suitable sensor of the kind described in further detail in U.S. Pat. No. 4,884,549. The sensor therein is constructed as a pressure sensor, which is disposed in a line between the pump and an injection nozzle. To that end, the high-pressure line must be opened up in order to place a sensor in it, which involves increased expense for pressure resistance and pressure tightness of the system. If a leak occurs, the system fails.